1. Field of the Invention
The present invention relates to an ink jet head of the type wherein ink droplets are ejected from an ink liquid plane by utilizing the effect of collective concentration of a series of waves propagating in ink. Further, the present invention relates to an ink jet apparatus having the foregoing type of ink jet head used therefor.
2. Description of the Prior Art
An ink jet recording apparatus, which is one of the most widely known as apparatuses using an ink jet head, has many advantages that it generates little noises, it can be operated at a low running cost, it can be constructed with small dimensions, and a color printing operation can easily be performed therewith. Owing to the aforementioned advantages, many ink jet recording apparatuses of the foregoing type are put in practical use as information output units each constructed in the form of a printer, a copying machine, a facsimile apparatus or the like.
The ink jet head generally used for the ink jet recording apparatus includes a plurality of ejecting ports (hereinafter referred to also as orifices) each having a diameter ranging from 20 .mu.m to 300 .mu.m. In this connection, reduction of the reliability which may occur in the ink jet head has been mostly attributable to malfunctions of the orifices as noted below. Typically, the malfunctions of the orifices arise such that each orifice is clogged with foreign materials such as dust particles or the like, the viscosity of ink is increased in each orifice inclusive of the peripheral part thereof, and each orifice is deformed. In such case as mentioned above, there additionally arises another malfunction in that a quantity of ink to be ejected from the orifices is reduced, and moreover, the ink is incorrectly ejected from the orifices.
In view of the conventional ink jet head constructed in the above-described manner, a proposal has been made with a so-called nozzleless head having no orifice used therefor. An example of the nozzleless head is constructively realized in the form of an acoustic ink jet head such that ink droplets are ejected from an ink liquid plane in the ink jet head by utilizing the effect of collective concentration of a series of waves propagating in ink. A basic principle of ink ejection of the foregoing type has been disclosed, e.g., in IBM Technical Disclosure Bulletin, Vol. 16, NO. 4, September 1973, p. 1168.about..
A so-called acoustic ink jet head of the foregoing type is constructed such that a series of pressure waves propagating in the ink are collectively concentrated at a specific spot in the ink jet head. With this construction, the number of dots capable of being simultaneously recorded on a recording medium such as a sheet of recording paper or the like by ejecting ink from the foregoing spot is limited only to one. For this reason, in contrast with other type of ink jet recording apparatus, it is necessary that the acoustic ink jet head is displaced relative to the recording medium at a higher speed.
However, in the case that a high speed recording operation is achieved by shooting onto the recording medium ink droplets ejected from the ink jet head while the recording medium which is immovably wound around a platen (drum) is rotated at a high speed, there sometimes arises an occasion that an air stream generated by the rotation of the platen for the displacement of the ink jet head relative to the recording medium causes the deflection of flying of ejected ink droplets each having a very small volume to be deviated away from the normal direction. This induces a problem that the position where the ink droplets are shot onto the recording medium is dislocated away from the normal position, resulting in a quality of each of recorded items such as characters, images or the like being degraded.
Since the number of dots capable of being simultaneously recorded on the recording medium with the ink droplets ejected from the ink jet head is limited only to one as mentioned above, it is necessary that the ink jet head is displaced relative to the recording medium during each recording operation at a high speed much more than that of other type of ink jet recording apparatus. Due to the foregoing necessity, a specially designed mechanism for displacing the ink jet head relative to the recording medium at a high speed is additionally required, resulting in a product of ink jet apparatus being unavoidably constructed with larger dimensions.